1. Field of the Invention
The present invention relates generally to spread spectrum (CDMA) communication systems and more specifically to a path searcher for use in a spread spectrum receiver for detecting delay characteristics of a plurality of communication paths for a diversity demodulator such as RAKE demodulator by taking correlation between a replica of a scrambled synchronization code and a received spread spectrum signal.
2. Description of the Related Art
Diversity combining is a well known technique in the art of spread spectrum systems to achieve gain of a received signal by combining component signals of different communication paths. This is achieved by the knowledge of individual path delays. In order to determine the individual path delays, a scrambled synchronization code is transmitted as a timing message. At the receiving site, the sync code is detected by taking correlation between the received signal and a replica of the scrambled sync code. Correlation values of the individual communication paths represent their delay characteristics. Since the correlation values must be obtained on a chip-by-chip basis, the amount of computations is significant and places a heavy burden on hardware. For example, if the scrambled sync code has “P” symbols and the number of chips per symbol is “S”, and correlation is taken at “T” points, multiplying and summing operations must be performed “P×S×T” times for detecting a sync code.
In a prior art base station receiver of spread spectrum communication network, the correlation technique requires the use of T correlators for each mobile user, with a total number of m×T correlators for each base station.
A technique is known to reduce this number by storing a P×T chip length of a received spread spectrum signal in a memory and repeatedly reading the stored data for correlation. However, a high capacity memory is required to hold this amount of information.